The prototype of The Flintstones is of the US version, which surprised me a bit considering that this was developed in Japan. The prototype appears to be pretty much the same as the final version, except for one thing - the prototype is full of slowdown. If you look at the animations below, Fred appears to run about twice as fast in the released version. However, the timer runs exactly the same as in the final version, meaning that you can easily run out of time, even in the first few levels.

Prototype

Released

Looking at the binary in a tile viewer, the graphics appear to be compressed differently between the prototype and the final. This may account for why the binary is 41% different (though at least some of that is due to data offsets). However, this does not change the visuals, as far as I can tell. Perhaps the slowdown is caused by an inefficient decompression algorithm. If you look carefully at the gifs above, you will also notice that the way the top stats and Fred's club appear are different between the prototype and final. In the prototype, they all appear at once, while in the final version, different elements appear in different frames.

Below, I show the difference between the prototype and released version using a tile viewer. These appear to be graphics tiles (though after playing through the entire game, I was not able to find out where they are in the game), but they look different, and there is an offset in the binary itself.

Prototype tiles

Released tiles

The only real difference in the game that I found besides the slowdown was the admission for the Park. The sound test option also has 35 tracks (compared to 21 in the released version), though there definitely are repeated and blank tracks in that mix.

Prototype: 30 clams

Released: 10 clams

Prototype cartridge (apparently the cart is glued shut, so no PCB scan!)